In an air conditioner, a refrigerator, and the like, an oil separator is installed in a discharge circuit to separate the oil included in the gas discharged from the compressor. Examples of oil separators conventionally known include a cyclone-type oil separator that causes a vortex to develop in the gas that includes the oil, and separates the oil using centrifugal force. Patent Document 1 discloses an oil separator in which a gas outflow pipe is inserted and installed in a center of a separator main body having an inlet pipe in a tangential direction connected thereto, and a multiplicity of auxiliary outflow holes are provided on an outer circumferential surface thereof. In such an oil separator, the auxiliary outflow holes are each provided with a hood having an opening formed on a frontward side in a swirling direction of the vortex. Further, Patent Document 2 discloses an oil separator in which an inlet pipe is connected to a shell having a gas outflow pipe inserted and installed in its center so that a tangential line of an outer circumferential side of a curved pipe portion of the inlet pipe matches a tangential line of an inner wall of the shell.
Further, examples of disclosed oil separators that have been reduced in size and built into a compressor include an oil separator in which a separation cylinder is integrally formed with a compressor housing, and a gas outlet holes is provided inclining toward a lower end side of the separation cylinder with respect to an axial line of the separation cylinder, as illustrated in Patent Document 3. Furthermore, examples of disclosed oil separators integrated with a compressor include an oil separator in which a separation cylinder is integrally provided with a compressor housing, a separation pipe is installed in a center thereof, an inner circumferential separation cylinder having a multiplicity of communication holes is installed in an inner circumferential bottom region of the separation cylinder, and an annular space is formed between the inner circumferential separation cylinder and the separation cylinder, thereby ensuring that the separated oil is introduced downward, as illustrated in Patent Document 4.